Figure 5. Voltage and Ca²⁺ even beat clamps for the single-cell cAF_alt model.

Traces of transmembrane potential (V_m, row 1), intracellular Ca²⁺ ([Ca²⁺]_i, row 2), and SR Ca²⁺ ([Ca²⁺]_SR, row 3) from two consecutive beats are superimposed to show alternans between even (red) and odd (blue) beats. Column 1: the unclamped cAF_alt cell paced to steady state at 400-ms CL displayed alternans in V_m and Ca²⁺. The red traces depicted in column 1 were used to clamp V_m (column 2), [Ca²⁺]_i (column 3), or [Ca²⁺]_SR (column 4). Alternans persisted when V_m or [Ca²⁺]_i is clamped, but clamping [Ca²⁺]_SR eliminated alternans.